Mobile communication devices can be used for communications while being exposed to different environmental conditions. The environmental conditions can largely influence the quality of communications, wherein two types of noise sources are typically considered. At the far-end side, noise is captured by the far-end microphone together with the desired voice component and is transmitted to the near-end side. At the near-end side, voice intelligibility may be affected by near-end noise, i.e. nearby noise sources masking the earpiece audio signal.
Enhancing the quality of a conversation, which is disturbed by noise, is conventionally addressed at the far-end side by the use of different audio signal processing techniques, such as noise cancellation, noise suppression, or beam-forming. A drawback of these techniques is, however, that the enhancements are only applied to the microphone signal at the fear-end side, which is then transmitted to the near-end side where the participant gets all the benefits. At the other side, no enhancements may be noticed.
Furthermore, adaptive gain or equalization control techniques can be applied on the near-end side. These techniques enable an adaptive gain or equalization control of the earpiece audio signal as a function of local background noise magnitude and earpiece audio signal statistics, wherein the loudness of the earpiece audio signal is adjusted in a frequency-dependent manner such that it is not masked by the local background noise. However, assumptions on human perception and voice intelligibility are applied in order to compare spectral components of both the earpiece audio signal and the local background noise, which makes these techniques complex and slow while adapting to changing noise magnitudes. In addition, complex voice activity detection (VAD) on the microphone audio signal is used in order to estimate the background noise magnitude only when the near-end participant is silent.
In F. Felber, “An automatic volume control for preserving intelligibility”, 34th IEEE Sarnoff Symposium, 2011, an adaptive gain technique for earpiece audio signals is described.
In A. Goldin, M. Tzur Zibulski, “Sound equalization in a noisy environment”, Audio Engineering Society Convention 110, 2001, an equalization control technique for earpiece audio signals is described.
In B. Sauert, F. Heese, P. Vary, “Real-time near-end listening enhancement for mobile phones”, IEEE International Conference on Acoustics, Speech, and Signal Processing, 2014, a further equalization control technique for earpiece audio signals is described.